1. Field of the Invention
The present invention relates to a control device for a mobile body, such as a legged mobile robot.
2. Description of the Related Art
As a mobile body provided with a base body and a moving mechanism which moves the base body on a floor surface, a legged mobile robot, for example, is generally known. In the legged mobile robot, its legs correspond to the moving mechanism and its body corresponds to the base body.
In the legged mobile robot, for example, as a technique for enhancing the stability of a posture of the robot, the technique disclosed in Published PCT International Applications WO2003/061917 (hereinafter referred to as patent document 1) or the like has been previously proposed by the applicant of the present application. According to the technique, a state amount deviation, which is a deviation of an actual posture of the body of a robot from a desired posture, is observed. Then, an operational moment (an operational moment about a desired ZMP) to be additionally applied to the robot is calculated according to a PD law (proportional-differential law) from an observed value of the state amount deviation as the required feedback manipulated variable (control input) required to converge the state amount deviation to zero. Further, the operational moment is divided into an actual robot operational moment to be directly applied to an actual robot and a model operational moment to be applied to a robot in a dynamic model for generating a desired gait of the robot. In the actual robot, the position and posture of the feet of both legs of the actual robot are corrected according to the position and posture of the feet in a desired gait by a compliance operation control such that an actual robot operational moment is generated about a desired ZMP. In the dynamic model, a desired gait of the robot is generated such that a model operational moment is generated about the desired ZMP.
Thus, in the case where the actual posture of the body of the robot deviates from a desired posture due to a disturbance or the like, a floor reaction force moment for eliminating the deviation is applied to the robot.
As disclosed in patent document 1, according to the technique in which the required manipulated variable (the operational moment) for converging the state amount deviation to zero is determined by the PD law, a gain coefficient applied to the observed value of a state amount deviation and a gain coefficient applied to the temporal change rate (a differential value) of an observed value of the state amount deviation are usually set to fixed values that are determined beforehand.
In this case, according to the knowledge of the inventor of the present application, when the robot is moved in a gait (e.g., a walking gait) that maintains the body of the robot at a substantially constant height (a vertical position), the posture of the body of the robot can be smoothly restored to a desired posture by using the operational moment determined by the PD law as described above.
However, it has been found that, in the case of a gait involving vertical motions of the body, as in the case where the robot runs, if the posture of the robot body is feedback-controlled on the basis of the operational moment determined by the PD law using the fixed values of the gain coefficients as described above, then the actual posture of the robot body frequently overshoots or undershoots a desired posture due to a change in the inertial force produced in the body (consequently the robot) caused by up and down motions of the body.